TRANSFORMATION OF DISLOCATION PATTERNS IN FATIGUED COPPER SINGLE-CRYSTALS

The transition from the so-called matrix to persistent slip bands (PSB s) during the fatigue of copper single crystals and the transition of the dislocation arrangement of PSBs formed at 300 K to that characteri stic for a deformation temperature of 77 K have been investigated by c yclic deformation tests and transmission electron microscopy. Strain l ocalization occurs well before the first fragments of the typical ladd er-like dislocation arrangement of PSBs can be identified. The results indicate that the motion of dislocation walls plays an important role in establishing the ladder-like dislocation arrangement. After a shar p decrease of the deformation temperature at constant amplitude of res olved plastic shear strain, only a certain volume fraction of the PSBs remains active, but with a larger intrinsic amplitude of plastic shea r strain.